Crosslinking organo-polysulfide rubber



Patented Mar. 17, 1953 CROSSLINKING ORGAN O -POLYS'ULFIDE RUBBERTheodore A. Te Grotenhuis, Olmsted Falls, and Gilbert H. Swart, Akron,Ohio, assignors to The General Tire and Rubber Company, Akron, Ohio, acorporation of Ohio No Drawing. Application September 21, 1949, SerialNo. 117,067

2 Claims. (Cl. 260-791) This invention relates to the production of asynthetic rubberlike material. It particularly relates to a rubberyreaction product of saturated and unsaturated organic compounds withinorganic polysulfides.

Rubberlike reaction products of alkaline polysulfides and eithersaturated or unsaturated organic compounds having two carbon atoms witha substituent capable of being split 011 during the reaction haveheretofore been proposed and manufactured. Those condensation product ofalkaline polysulfides with saturated organic compounds such as alkylenedihalides, e. g., ethylene dichloride, propylene chloride, or withdichloroethers, are extremely resistant to chemicals, solvents andaromatic oils but have relatively low tensile strength, elasticity andabrasion resistance. They are especially undesirable for several usesbecause they have poor resistance to cold flow and only fairvulcanizability and general workability, as distinguished from some ofthe other commercial synthetic rubbers.

It is an object of the present invention to provide a vulcanizablerubbery reaction product or condensation product of alkalinepolysulfides and organic compounds, which product is extremely resistantto light, chemicals and the like but has less tendency for cold flowthan have the reaction products of compounds such as olefin dihalidesand alkaline polysulfides heretofore prepared.

It is a still further object of the present invention to provide amethod of making a rubbery product utilizing an inorganic polysulfide,which product has high resistance both to chemicals as well as to coldflow.

Other objects will be apparent from the following description of theinvention.

In our prior application Serial No. 476,214, filed February 17, 1943,part of which matured into United States Letters Patent 2,445,191, wedescribed the crosslinking of polysulfide rubbers by suitablyincorporating spaced crosslinking groups selected from hydroxyl, aminoand olefine groups into the polymer chain, and reacting such groups withan appropriate crosslinking compound, which may be dicarboxylic acidanhydride thereof, di-isocyanate or vulcanization agent for olefinicpolymers such as sulfur. The crosslinking groups were disclosed as beingspaced in the average polymer chain to provide but one crosslinkinggroup for each ten up to a high limit of five hundred carbon atoms ofthe polymer. The present application is a continuation-in-part of our application Serial No. 708,936, filed November 9,

1946, now abandoned, and copending with the application that maturedinto United States Letters Patent 2,445,191.

In accordance with the present invention, rubberlike polymers ofimproved resistance to cold flow after vulcanization are obtained byreacting an alkaline polysulfide, which has at least two and preferablyabout three to five sulfur atoms per molecule, with a mixture of one ormore saturated base compounds and one or more substitute compounds orcrosslinking compounds, i. e, organic compounds containing at least onehydroxyl or amino group in addition to the substituents which areafiected by reaction with the inorganic polysulfide. The base compounds(this term is herein used to designate compounds havin an absence ofgroups for crosslinking) are preferably entirely saturated and arepresent in major proportion and have two, and preferably only twosubstituents such as halogen which are capable of being split oii duringthe polymerforming reaction. These substituents are connected todifferent connected carbons. The substituted or crosslinking compounds(having a hydroxy and/or an amino group for crosslinking) are present inonly minor proportions to provide for cross linkage during vulcanizationwith agents effecting cross linkage between said substituted (hydroxyland/or amino) groups. Since these groups apparently may be in largemeasure reacted during vulcanization with dicarboxylic acid, anhydrideor chloride, or di-isocyanate, there is no appreciable decrease inchemical resistance of the rubbery material. The substituted orcrosslinking compounds like the base compound or compounds contain twogroups, such as halogen, which are split on? during the polymer-formingreaction.

The amount of substitute or crosslinking compounds for crosslinkingshould preferably be much less than the amount of base compound. Themore desirable amounts or molar proportions vary with the molecularlength or molecular weight of the compounds, exclusive of substituents,and with the number of crosslinking roups in the molecule ofcrosslinking compound. To materially decrease cold flow, the proportionsof the materials should be chosen so that at least one such crosslinkinggroup is present for each 400 or 500-chain carbon atoms in the finalunvulcanized rubberlike molecules, and as much as one such group foreach 10 or 15 carbon atoms may be used, although at the higherproportions of crosslinking compound resistance of the polymer tochemicals may be somewhat less. Preferably, the amounts of thesubstituted and unsubstituted compounds are chosen so that there is onecrosslinking group selected from the group consisting of hydroxyl andamino groups for about each 100 to 300 carbon atoms.

It is desirable that the base compound and the cross-linking compoundsbe comiscible or cosoluble in the proportions used and that thecompounds have some solubility in the aqueous media containing theinorganic polysulfide. For the best results, the saturated andsubstituted compounds (each containing two halogen or oth-. er groupssplit off by contact alkaline polysuk fides) should have solubilities inthe aqueous. media containing the inorganic polysulfide in about theproportions of their concentrations in the mixture, so that reactivityof the base and crosslinking compounds will be more nearly related totheir concentration and a relatively uni-r form distribution of thecrosslinking groups will occur within the rubber molecules. When theunsaturated compound is insufficiently soluble in water, the solubilitymay be adjusted to the re-v quired magnitude by incorporating varyingamounts of a mutually miscible solvent, such for example as a loweralcohol, ketone, etc., with the materials containing the twosubstituents, such as halogen, split off in the polymer-formingreaction.

The saturated compounds which preferably furnish the major portion ofthe hydrogen and carbon in the rubbery polymers of the present.invention may be: an olefin dihalide, e. g. ethylene propylene orbutylene chloride or bromide; a disubstituted ether, e. g.beta-beta-dichlorodiethylether; or other saturated compounds con tainingtwo and only two halogen or other substituents, one of which is attachedto each of; two different carbon atoms, which substituent is split oifby reaction with the polysulfide. saturated compound, such asdichloropropylene. (epidichlorohydrins, allylene dichloride)vdichloroethylene, butadiene dichloride, and homologues of dichloroanddibromo-propylenes having substituents attached to different. carbonatoms,

which are split oif during the reaction withthe.

alkaline polysulfides, may also be present as part. of the basecompound, but are preferably absent,

The crosslinking compound or compounds as aforementioned contain inaddition, to t e two substituents, such for example as; halogens, etc.that are to be reacted with the inorganic, poly-- sulfide, at least onemember of the group consisting of hydroxyl and amino groups. Examples ofsuitable compounds which contain suchv crosslinkine groups for reactionwith, one or morecrosslinking compounds are: 2-,4-dich1oroaniline;ZA-dibromoaniline; alpha-beta-glycerol dichlo rohydrins;2-amino-1,3-dichloropropane; dichlorophenols;2-amino-3-hydroxy-1,4-dichlorobutane; and the corresponding compoundscontaining bromine in place of chlorine; etc. In fact any hydroxy and/oramino dichloro-aliphatic. or aromatic compound may be used, but thosewhich are aliphatic are preferred. These compounds in admixture withother dichlorodisubstituted compounds are reacted with the inorganicpolysulfides to produce solid condensation products which arevulcanizable by reac-. tion with suitable crosslinking agents, milled.into. the rubbery material.

As a crosslinking agent to be mixed with the rubbery polymer orcondensation product during the compounding thereof, any materialwhichis. a polycarboxylic acid in liquid water may be used.

Some un- Such materials are the polycarboxylic acids themselves, theiracid anhydrides, and their acid chlorides. The latter two materials arecompletely transformed into the corresponding acids. Esters and amides,which maybe considered to be hydrolyzed to a slight extent in water, arenot considered as materials that are dicarboxylic acid in liquid water.Any organic polyisocyanate (containing a plurality of N=C=O radicals)maybe used with the rubbery polymers containing the spaced hydroxy oramino groups in place of or inconjunction with the polycarboxylic acids,etc.

Examples of: suitable materials which in liquid water are dicarboxylicacids are: (1) the dicarboxylic aromatic acids such as phthalic acid,terephthalic acid, dicarboxylic naphthenic acid, etc.; (2) thedicarboxylic aliphatic acids including saturated alkane dicarboxylicacids, such for example as succinic, malonic and sebacic acids; (3) theunsaturated aliphatic. or alkylenyl dicarboxylic acids such for exampleas the alpha-s beta unsatur-ated dicarboxylic acids, maleic,methylmaleic, ethylmaleic, fumaric, citraconic glutaconic and itaconicacids, etc.

The dicarboxylic aliphatic: acids themselves may even have a hydroxygroup present, such as malic acid. Such acids are not. as desirable as.those in which the carbox-yls are attached to hydrocarbon groups andshould be used in larger quantities.

Anhydrides of any of the above acids are preferred to the acidsthemselves and the acid ch10. rides may even be used, although such are;objectionable from the handling standpoint due to. the decompositionproducts involved.

Since in the case of organic poly-isocyanates. it. is. the isocy-anate.groups alone that enter into reaction, it matters little what. isbetween these groups as. spacers, except that. it is an organic. group.to provide increased compatibility with the; polymer and space betweenthe functional groups. to permit the two groups. of a single molecule toreact. with two polymer molecules.v Examples of the polyisocyanateswhich may be used, are the. aliphatic di-isocyanates, includingalkylene. diisocyanates such as ethylene, hexylene, butylene and decyldi-isocyanates; having the, isocyanate; groups on difierent, carbonatoms. The. aromatic; naphthalene di-isocyanates, and the alkyl oralkylene di-isocyanates are preferred, however,

The, alkaline polysulfide which is usually used for reaction withhalogen-substituted compounds. may be prepared in any suitable, way, asby boiling a slurry of lime or alkali metal hydroxide, for several hourswith sufiicient sulfur to. form a, polysulfide of at least four atomsto. the molecule; by fusing sulfur with di'sodium disulfid'e; etc, Thehigher sulfur concentration tends, upon reaction with the organicconstituents, to. form the. softer rubberlike products. Except for thesub.-. stitution of the crosslinking compounds, in the, above-designatedproportions. for part. of. the. other disubstituted organic materials,the preparation of the polymer may be. identical with that described inthe. Patrick United States Letters Patentv 2,195,380, 2,221,650,2.363514% 2,363,615, etc.

The bifunctional crosslinking agents; function to connect, the hydroxyor amino, group of two molecules together by direct chemical bonds. 1mol of dicarboxylic. acid andv 1 mol, of di-isocyanate are thereforeobviously chemically equiv-. alent to 2 mols of hydroxy and/orami'no,groups in the polymer. The reactions are well understood in the art, andin the polymer, as elsewhere, the bifunctional crosslinking agentsshould for best results be used in a total amount about equivalent tothat theoretically required to react the desired number of the hydroxyand/or amino groups. A slight excess is sometimes desired in a reactionof this esterification type unless drastic conditions are present, andin a solid polymer not all of the crosslinking agent may be in positionto react. Since the number of crosslinks need be very few in number toeffect vulcanization of a high molecular weight polymer and the polymersmay be made to vary greatly in molecular weight, no universal definitelower limit may be given where vulcanization initially occurs. Even verysmall amounts of bifunctional crosslinking agents, however, such as theorganic polyisocyanates and organic polycarboxylic acids, have aperceptible vulcanizing effect on the polymers and the amount ofcrosslinking varies as the amount of these crosslinkers increase untilall the hydroxy groups and equivalent amino groups are reacted. Thecrosslinking agent is in most cases preferably used in around the samepercentages as are usual rubber vulcanizing agents, which are ordinarilypresent in amounts of about .1% to 5% of the weight of the rubberypolymer. The optimum amount depends on the molecular weight of thecrosslinking agent and is obviously higher for higher molecular weightdicarboxylic acids. The crosslinking agent may also be present inexcess, say as high as of the rubbery polymer, without exerting muchadverse eifect, particularly when the amount of hydroxy groups is at thehigher concentrations so that a sufficient number of crosslinks isformed even though some of the bifunctional reactants only partiallyreact. Considerable excess of the bifunctional reactants obviouslydetracts from the crosslinking by such competing monofunctionalreaction, however.

The products produced as herein described are, after removal ofimpurities, masticated with carbon black and vulcanizing agents.

The following examples, in which parts are by weight, illustrate thepresent invention.

Example 1 500 grams of hydrated sodium sulfide are dissolved in about 1liter of water and the solution boiled with 200 grams sulfur. Thepolysulfide formed, which has the formula NazS4-5, is diluted with waterto have a specific gravity of about 1.25. About 250 grams of ethylenedichloride and about '7 grams of glycerol dichlorohydrin (the molarequivalent of about 6 or '7 grams of butadiene dichloride) areintimately mixed with about 100 grams of ethyl alcohol and the mixtureis gradually added to the polysulfide solution with vigorous stirring.This mixture is heated at about '70 or 80 C. in a vessel having a refluxcondenser, the reaction being completed in about two hours. The plasticproduct remaining after the withdrawal of the liquid is washed withwater. After drying, it is mixed with parts of carbon black (based on100 parts of the rubber plastic), about 8 parts of zinc oxide, and about5 grams of phthalic acid anhydride (about that required to completelyreact with the hydroxyl groups of the 7 grams of glyceroldichlorohydrin). The compounded material when cured has substantially notendency for cold fiow and has excellent resistance to chemicals.

Example 2 150 parts of ethylene dichloride are mixed with about 10 partsof propylene dichloride and 25 parts of glycerol dichlorohydrin. Themixture is added slowly, with stirring, to a dispersion of about 260parts of sodium polysulfide in 1100 parts of water, containing about 5parts of a stabilizing agent such as sodium alkyl naphthalene sulfonate,and about 12 parts of freshly precipitated magnesium hydroxide. Thetemperature of the reaction mixture is maintained at around 70 C. withconstant stirring during the first part of the reaction and graduallyraised, until C. is reached. The latex is coagulated in the usual mannerwith salt and sulfuric acid, and the coagulum dried to obtain a rubberyproduct. The rubber product is compounded in accordance with thefollowing formula, in which the parts are by weight:

The above ingredients are mixed in usual order on a cold mill, themaleic anhydride, which serves as a crosslinking agent as abovedescribed, being added last. The product is cured at the usual rubbervulcanizing temperature of 300 F. for about fifteen minutes. The curedproduct exhibits very little cold flow compared to the usual curedolefin polysulfide rubber products.

While the base compound is preferably entirely saturated and inasmuch asunsaturation (double bonds) apparently does not enter into anycrosslinking reaction with the discarboxylic or crosslinking agents,etc, but merely decreases chemical resistance of the polymer, the basecompound may contain unsaturated groups or may be a mixture of saturatedand unsaturated dihalides, etc.

This application is a continuation-in-part of our prior applicationsSerial No. 476,214, filed February 17, 1943, and Serial No. 708,936,filed November 9, 1946.

In the above examples, the crosslinking agent used may be substituted inwhole or in part by a molar equivalent of any of the above isocyanates,or above-designated acid anhydrides, or acids themselves withsubstantially equivalent results. The amount of crosslinking agent andthe proportions of crosslinking groups in the polymer may be variedwithin the limits above described.

Although the invention may be employed in various ways, only preferredembodiments have been illustrated and described. Other embodiments maybe made within the invention as provided by the patent statutes.

What we claim is:

1. A method of preparing a rubbery organic polysulfide polymer that isvulcanizable with polycarboxylic acid and anhydrides thereof to theelastic state generally similar to that of soft vulcanized rubber, saidmethod including the steps of condensing an excess of an alkali metalpolysulfide with a mixture of a glycerol dichlorohydrin and a loweralkylene halide to form an elastomeric product, said glyceroldichlorohydrin being present in minor proportion relative to saidalkylene halide, to provide one hydroxyl group for 10 to 500 carbonatoms of said polysulfide polymer.

2. A product prepared according to claim 1.

THEODORE A. TE GRO'I'ENHUIS. GILBERT H. SWART.

(References on following page)

1. A METHOD OF PREPARING A RUBBERY ORGANIC POLYSULFIDE POLYMER THAT ISVULCANIZABLE WITH POLYCARBOXYLIC ACID AND ANHYDRIDES THEREOF TO THEELASTIC STATE GENERALLY SIMILAR TO THAT OF SOFT VULCANIZED RUBBER, SAIDMETHOD INCLUDING THE STEPS OF CONDENSING AN EXCESS OF AN ALKALI METALPOLYSULLIDE WITH A MIXTURE OF A GLYCEROL DICHLOROHYDRIN AND A LOWERALKYLENE HALIDE TO FORM AN ELASTOMERIC PRODUCT, SAID GLYCEROLDICHLOROHYDRIN BEING PRESENT IN MINOR PROPORTION RELATIVE TO SAIDALKYLENE HALIDE, TO PROVIDE ONE HYDROXYL GROUP FOR 10 TO 500 CARBONATOMS OF SAID POLYSULFIDE POLYMER.